Re: [PATCH 3/3] dt-bindings: hwmon: max31790: Add pwmout-pin-as-tach-input property

From: Chanh Nguyen
Date: Tue Mar 26 2024 - 06:34:36 EST




On 18/03/2024 16:53, Chanh Nguyen wrote:


On 12/03/2024 00:34, Rob Herring wrote:
On Mon, Mar 11, 2024 at 06:13:47PM +0700, Chanh Nguyen wrote:
Add pwmout-pin-as-tach-input property.

Signed-off-by: Chanh Nguyen <chanh@xxxxxxxxxxxxxxxxxxxxxx>
---
  Documentation/devicetree/bindings/hwmon/max31790.yaml | 11 +++++++++++
  1 file changed, 11 insertions(+)

diff --git a/Documentation/devicetree/bindings/hwmon/max31790.yaml b/Documentation/devicetree/bindings/hwmon/max31790.yaml
index 5a93e6bdebda..447cac17053a 100644
--- a/Documentation/devicetree/bindings/hwmon/max31790.yaml
+++ b/Documentation/devicetree/bindings/hwmon/max31790.yaml
@@ -25,6 +25,16 @@ properties:
    reg:
      maxItems: 1
+  pwmout-pin-as-tach-input:
+    description: |
+      An array of six integers responds to six PWM channels for
+      configuring the pwm to tach mode.
+      When set to 0, the associated PWMOUT produces a PWM waveform for
+      control of fan speed. When set to 1, PWMOUT becomes a TACH input
+    $ref: /schemas/types.yaml#/definitions/uint8-array
+    maxItems: 6
+    minItems: 6

Seems incomplete. For example, fan tachs have different number of
pulses per revolution, don't you need to know that too?

There's a common fan binding now (or pending). You should use that and
this property won't be needed.

Rob

Thank Rob,

I checked in the Documentation/devicetree/bindings/hwmon/fan-common.yaml. I found the tach-ch property, but it seems define the tach channel used for fan.

  tach-ch:
    description:
      The tach channel used for the fan.
    $ref: /schemas/types.yaml#/definitions/uint8-array

I would like to define a new vendor property to configure the PWM-OUT pin to become a TACH-IN pin. So I introduce the "maxim,pwmout-pin-as-tach-input" property. Please help me share your comments!

Hi Guenter and Rob,

I'm preparing for patch v2. I'm looking forward to hear your advice. Should I use the "tach-ch" property (a common fan property) or define new vendor property ("maxim,pwmout-pin-as-tach-input") for my purpose?

Thank you very much!
Chanh